JPS58204538A - Method of fabricating metal silicide-polysilicon bilayer structures on substrates containing integrated circuits - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for creating structures by reactive ion etching in bilayers of metal silicide and polysilicon on silicon substrates containing integrated semiconductor circuits. In many cases, it is advantageous for the silicon substrate to be covered with an insulating film, and it is placed in a flat plate reactor and etched using a photomask. Do the following.

Metal silicides have become increasingly important in the fabrication of highly integrated MO8 circuits. A possible field of use is as a low-resistance material for conductor tracks and gates in polysilicon gate technology. In this case, the polysilicon is generally not replaced by silicide, but silicide is added by placing the silicide on a layer of doped polysilicon. Creating microstructures in such double layers is a complex etching process given that a series of boundary φ conditions must be considered in the fabrication of integrated circuits.

It is an object of the present invention to solve such etching problems.

Consideration 1) in the etching process when manufacturing integrated circuits
Figure 1 shows the boundary conditions that must be met in detail (
I will explain. Here, 1 is the silicon substrate, 2 is 5i021 on the substrate surface, and 3 is the n+ type doped polysilicon layer%.
4 is a silicide layer, 5 is a photosensitive resin layer serving as an etching mask, and 6 is a first boron silicone layer.

1, 7 is an oxide insulating layer on the gate. In the south side below, all of these numbers indicate corresponding parts.1 The vertical arrows drawn in FIG.

At arrow 10, 5i02 or similar insulation (7
First, a high degree of selectivity is required. Double layer 3゜4 and 51
The thickness ratio of 02 layer 2 reaches up to 20:1.

As indicated by arrow (1), a suitable shape is required at the edge of the ilt etching structure. Vertical end faces as shown in the figure are formed by anisotropic etching, or inclined surfaces are formed by inclined etching.

At arrow 12 there is a problem with double polysilicon gate technology (in order to avoid the risk of short circuits caused by etching residues on the edge of the first polysilicon gate).

At arrow 1:3 there is the problem of forming a contact or a buried contact of the double layer 3, 4 to the substrate 1.

In addition to solving these problems, the present invention includes the use of a photosensitive resin mask as an etching mask, which is not attacked during the etching process.

There is a purpose to do so. Furthermore, consider a phenomenon called the short channel effect! Furthermore, a high degree of corrosion uniformity is required in all parts.

Etching methods for polycrystalline silicide structures, which in most cases are silicides of molybdenum and tungsten, are already known. However, it has higher heat resistance at high temperatures than molybdenum and tungsten silicides,
Regarding the etching of tantalum silicide structures, which are extremely advantageous in terms of good adhesion to polysilicon, the literature (J.
Vac, Sci.

Technol, 1.7. (4) July/
Aug, l 980. p.

787-788).

According to this, silicides of titanium, tantalum, molybdenum, and tungsten can be plasma etched in a mixed gas of carbon tetrafluoride and oxygen. This etching is carried out partly in a tunnel reactor and partly in a parallel plate reactor under anodic bonding. In principle, these layers can be wet-etched, but the dimensional losses customary for wet etching occur in this case.

European Patent Application No. 0015403 describes various plasma etching methods for polysilicon, in which a mixture of hexafluoride ions (SF6), chlorine (012) and an inert gas is used. .

In these methods, only silicon is selectively etched, and 5
Very good selectivity is achieved when io2 and silicon nitride coexist. Furthermore, the corroded substrate is placed on a high-frequency application electrode, and directional etching is performed based on reactive ion etching.1 The created recess has vertical sidewalls, and the etching mask protrudes beyond the edge of this recess. You can avoid it.

The method mentioned at the beginning has already been proposed, but
There, sulfur hexafluoride is used as the etching gas, and the etching process is carried out in two stages with different corrosion rates. In this case as well, strict anisotropic corrosion is desired.

The method of the present invention surpasses prior art techniques in corroding metal silicide, borin recon two layers, and also eliminates the problem of slope etching or paragraphing between adjacent polycrystalline silicide conductor tracks in the double borin recon gate process. This solves the problem without causing a short circuit. These problems are indicated by arrows II, 12 and 13 in FIG.

The method according to the invention is characterized in that a mixed gas containing fluorine and chlorine is used as the reaction gas. For example, when an etching gas containing only fluorine, such as sulfur hexafluoride, is used, an overhang is formed in the corroded area.

Furthermore, when chlorine is used as the etching gas, the corrosion rate becomes extremely low, especially in the case of tantalum silicide layers. It is also within the scope of the invention to use a gas mixture consisting of sulfur hexafluoride (SF6) and chlorine (SF2).

It is also possible to use fluorinated hydrocarbons substituted with chlorine atoms, such as monochlorotrifluoromethane (cazy3) or dichlorodifluoromethane (OCl2F2).

In a particularly advantageous embodiment of the invention, the thickness is approximately 200 mm.
n m tantalum silicide layer (tantalum to silicon ratio 1:
A double layer consisting of 2) and a 300 nm thick n+ doped polysilicon layer is used.

Other embodiments of the invention are shown in claims 2 and below.

The details of the invention and its advantages will be explained with reference to embodiments and FIGS. 2 to 8.

FIG. 2 shows a cross section of a structure made by the method of the invention. This structure consists of a D-type tope (phosphorus or arsenic) polysilicon layer 3 provided on the surface of a silicon substrate 1 covered with a 20 nm thick 5102 layer 2, and a 200 nm thick polysilicon layer 3 on top of the silicon substrate 1.
It consists of a tantalum silicide layer 1 deposited on m. 5 is a photosensitive sebum layer used as an etching mask. The tantalum to silicon ratio is approximately 1 = 2, and the tantalum ratio is 30
Variations from % to 50% are allowed. FIG. 2 shows a structure aimed at strict anisotropic etching. This can be achieved, for example, by employing a two-step etching process, first etching the tantalum silicide layer 4 with a chlorine-free etching gas and then treating the poly/licon layer S3 in pure chlorine. With this method, the silicide polysilidine bilayer is etched with vertical edges completely without corrosion. The switching point from the first stage to the second stage can be determined, for example, by recording the intensity of the appropriate emission spectral line of the plasma. At the same time, in the second step it is possible to achieve a high polysilicon selectivity for 5it)2 of 30:1 or higher.

The situation in which the cross-sectional shape of the edge surfaces of the double layers 3, 4 is deformed depending on the composition of the etching gas mixture is shown in FIG. The horizontal axis represents the mixing ratio of sy6:ct2, and the vertical axis V represents the corrosion time tW (in minutes) of the double layer. The dashed line in the figure represents the relationship between corrosion time and gas composition. Structure A is the result of long-term corrosion without chlorine content, Structure A is the result of extremely short corrosion time, and Structure C is the product with a mixing ratio of SF6:c.
This is due to the shortest corrosion time at 12=2:1. The structure's cross-sectional shape is still usable. The structure θ was made with a mixture ratio of SF5:C42=5:15°, and strong wrap-around corrosion occurred in the silicide.

When the mixture ratio is SF6:C72=5:15, the anisotropy that is better for the weir than this is obtained by lower gas pressure (approximately 10 m Torr).
=], 5 Pa).

In the case shown in FIG. 3, the gas pressure in the reaction vessel during etching was 6 to 9 Pa (=40 to 60 mTorr), and the high frequency power density was about 0.12 W//crn2.

Figures 4 and 5 show the corrosion rate (n m7m1 n), gas pressure (Pa), and high frequency power density (Wat t//
crn2). The arrows point to the conditions under which the described structure was created.

In the case of FIG. 4, the high frequency power is adjusted to 01'W/-, and the mixture ratio of the mixed gas is SF6:072:Hθ=12, . 5:
It was 8.5:20. The X-dashed line shows the selectivity of tantalum silicide, the 0-dashed line shows the selectivity of polysilicon, the open-dashed line shows the selectivity of polysilicon with respect to 5io2, and the 8-dashed line shows the selectivity of polysilicon with respect to 5102.

In FIG. 5 showing the relationship with high frequency power, the curves have the same meaning as in FIG. 4. In this case, the gas pressure in the reactor is 40
mTorr.

It has been established that the corrosion profile shown in FIGS. 6 and 7 is strongly related to the shape of the reactor, ie, the ratio of effective plasma volume to its total volume, when the gas mixture composition is constant.

This volume ratio affects the concentration distribution of various radicals in the plasma. In the structure shown in Figure 6, the ratio of the plasma active volume to the reactor volume is less than 1:20, and in the case of Figure 7, it is approximately 1:2, with half of the reactor volume being the active volume. ing. The important difference is that in Figure 6, the silicon compound (upper layer) undergoes anisotropic corrosion with respect to the photoresist mask at an SF6:ct2 ratio of t, whereas in Figure 7
In the case of the figure, the corrosion situation of silicides varies depending on the gas mixture ratio.
As shown in the figure, the corrosion changes from anisotropy to strong wraparound corrosion.

If the polysilicon silicide layers 3, 4 are to be in secure local contact with the /recon substrate, some corrosion of the substrate is inevitable (see arrow +3 in FIG. 1). This results in a high resistance between the polynosilicide layer and the substrate at the end of the manufacturing process.

1O:1, thereby keeping the erosion of the substrate to an extremely small amount. This situation is shown in Figure 8.

The figure shows the corrosion rate ratio of n+ borin recon vs. single crystal silicon or the selectivity of n+ borin recon vs. 5102 SF6:
It is shown in relation to the ct2a synthesis ratio. The erosion speed is Sccm
(expressed in standard tyn3 per minute). Standard conditions mean atmospheric pressure and specific temperature.

The curve with arrow 1'+ represents the selectivity and the curve with arrow 15 represents the corrosion rate. The symbol O indicates the measurement point.

Advantageous values for the gas mixture ratio SF6:O42 are from 5:15 to 2
:18 range.

It is also within the scope of the invention to carry out the structural formation of the double layers 3, 4 before the tempering heat treatment for polycrystallization of the silicide and for lowering the resistance. Before tempering, the silicide-polysilicon interface is much smoother than after tempering. This has the advantage that the switching point is clearly determined during two-step etching.

[Brief explanation of the drawing]

FIG. 1 is a drawing showing the points that need to be taken into consideration when manufacturing an integrated circuit, FIG. 2 is a cross-sectional view of a structure made by the method of the present invention, and FIGS. 3 to 5 show the optimum etching conditions. Figures 6 and 7 show the structures produced at various values of the reaction vessel volume to active plasma response ratio, and Figure 8 shows the structures produced therewith. Corrosion rate of n+ doped polysilicon relative to single crystal silicon The selectivity of polysilicon to 1, il ratio or 5i02 is shown in relation to the mixed gas composition. In each figure 1: silicon substrate, 2: 5102 @, 3 :n
+doped poly/recon layer, 4: silicide layer, 5: photosensitive resin etching mask. FIG 4 a b c l 5 [15Pa IG 5

Claims (1)

[Claims] 1) A peripheral plate containing an integrated semiconductor circuit is placed in a flat plate reactor (C), and a reactive gas (/ζ) is etched using a reactive gas mask. A method for forming a metal silicide/poly7 silicon layer structure on the surface of a substrate containing an integrated circuit using a mixed gas containing fluorine and chlorine as a reactive gas. 2) As a reactive gas Sulfur hexafluoride (SF6) and chlorine (
2. Process according to claim 1, characterized in that a gas mixture consisting of C62) is used. :)) 1 g of chlorine the method of. 4) A method according to any one of claims 1 to 3, characterized in that a double layer of tantalum silicide (TaSi2) and polysilicon is used. 5. A method as claimed in claim 4, characterized in that it comprises a layer of doped polysilicon of 1 nm. 6) When using a mixed gas of sulfur hexafluoride and chlorine, the mixing ratio of sF6 to ct2 should be set to 2 to cause wraparound corrosion.
;1, the gas pressure is adjusted to 6 to 9 Pa, and the high frequency power of one reactor is adjusted to 0.1 to (1.14 W/cm2). 7) When using a mixed gas of sulfur hexafluoride and chlorine, the etching process is divided into two stages to perform anisotropic etching. Etch with a mixture of hydrogen and chlorine gas,
Next is the poly method. 8) In order to cause wraparound corrosion to the poly/recon layer, when the mixing ratio of hexafluoride to chlorine is set to 1:1, adjust the ratio of the reaction gas volume in the reactor to the reactor volume to 1 = 20 or less. 1)) In order to cause wraparound corrosion in the tantalum silicide layer K 71 , when the mixing ratio of hexafluoride ions to chlorine is 1:1, the ratio of the effective reaction volume in the reactor to the reactor volume is [ The method described in any one of the scope of claims 1 to 7 of I Patent 1, which is characterized by adjusting 1=2. 10) Reactive ion etching is carried out before the tempering heat treatment necessary to transfer the metal silicide/borinlico/bilayer to crystalline form.
The method according to any one of Items 9 to 9. 11) A method according to any one of claims 1 to 10, characterized in that a rare gas such as helium is used as the transport gas.